Abstract Detail

There is increasing evidence that certain exotic species evolve invasiveness at some time point following introduction. The Callery pear (Pyrus calleryana Dcne. [Rosales: Rosaceae]) is a common ornamental tree that has begun invading old field and natural areas, sometimes creating dense, monospecific stands. Volunteer populations have been identified in 26 states, and the species is recognized as an invasive in ten states. The goal of this experiment was to document the occurrence of intraspecific hybridization, via crossing of genetically distinct cultivars, in the formation of invasive populations of Pyrus calleryana. Hybridization has been previously identified as a mechanism for evolution of invasiveness in introduced species by facilitating escape from genetic bottlenecks and/or creating novel genetic combinations that increase invasive potential. Using nine microsatellite markers, commercially available cultivars were characterized and found to be genetically distinct from one another. Parentage analyses of invasive individuals in populations in three states were performed to determine the most-likely parent pair of invasive individuals and the overall relative contribution of cultivars found in nearby putative parent populations. In multiple populations located across the introduced range, invasive individuals were found to be F1 or advanced generation progeny of cultivated individuals. Extensive admixture of cultivar genotypes was found in all populations. This new genetic admixture in the introduced range may ultimately serve to promote establishment and increase fitness in naturalized populations.